The use of aluminum parts in the automotive industry is now well established. Aluminum radiators, heaters, water pumps and engines are found in many late model passenger cars and other automotive vehicles. Most coolant or antifreeze compositions for use in such coolant systems contain one or more corrosion inhibitors. These corrosion inhibitors are utilized to prevent the deterioration of the aluminum and other metals in contact with the antifreeze.
Presently, perhaps the most cost effective corrosion inhibitor for aluminum is silicate. There are numerous patents and publications directed to the use of silicate as a corrosion inhibitor in coolant compositions. However, silicate is very pH sensitive and has a tendency to gel irreversibly. Thus, there have been many reported instances of deposits "dropping out" of coolants with high silicate levels. Silicate is also alleged to be somewhat aggressive on some foreign-made water pumps.
Several attempts have been made at stabilizing coolant compositions so as to prevent the fall out of gelled deposits. Various siloxanes have been proposed for this purpose.
1-hydroxyethylidene-1,1-diphosphonic acid or HEDPA is known in the art as a corrosion inhibitor for mild steel, and is currently available from Monsanto under the trademark DEQUEST (R) 2010. HEDPA may be prepared according to the following reaction: EQU RCOOH+2PCl.sub.3 +5H.sub.2 O.fwdarw.RC(PO.sub.3 H.sub.2)2(OH)+6HCl
where R=C.sub.1.
HEDPA has been shown to be rather aggressive against aluminum.
Other patents also relate to the use of phosphate compounds to prevent corrosion in aluminum and other metal-based systems containing coolant formulations. Carr, U.S. Pat. No. 4,707,286, relates to the use of certain organic phosphonate compounds and certain organic silicon compounds as stabilizers for coolant compositions.
Moran et al., U.S. Pat. No. 4,613,450, discloses corrosion inhibitors for protecting metallic surfaces which come into contact with water. The primary constituent of these corrosion inhibitors are fluorophosphate compounds.
Vukasovich et al., U.S. Pat. No. 5,000,916, is directed to the use of a molybdenum carboxylic compound and the use thereof as a corrosion inhibitor of steel and other metals in cooling water.
Jacob, U.S. Pat. No. 3,935,125, relates to a method and composition for inhibiting corrosion in aqueous systems, the composition including a mixture of amine pyrophosphate, an organophosphonate, and triazole.
A new class of compounds has now surprisingly been found to be extremely effective in controlling corrosive build-up on aluminum and other metals such as copper, brass, steel and solder. These compounds are 1-hydroxyoctylidene-1,1-diphosphonic acid (HODPA) and 1-hydroxydodecylidene-1,1-diphosphonic acid (HDDPA), and may be derived from the above reaction formula where R=C.sub.7 and R=C.sub.11, respectively. Accordingly, preferred starting materials include octanoic and dodecanoic acids, respectively. To date it is believed that neither HODPA nor HDDPA has been successfully utilized as a corrosion inhibitor in coolant compositions.